Ron-Sensei's Magnifying Glass

Genta visits the inn "Senninkyo" with Mr. Ron for his summer vacation homework, collecting insects. However, there is a youkai called Azuki Washing here, and it is said that every night you can hear the sound of washing azuki beans. "Such things are superstitions," said Genta, who was frightened, but Ron-sensei seemed to have noticed something...?